For those of you who have hiked with me, you know how much I love the herps. Summer is the time for herpetology; the branch of zoology that includes amphibians and reptiles. In our region, we have two orders of amphibians (Caudata – salamanders, and Salientia – frogs and toads, aka the anurans) and two orders of reptiles (Testudines – turtles, and Squamata – snakes and lizards).
Probably everyone has turned over rocks or logs and found a salamander. Chances are, you found a red-back salamander. These terrestrial members of the lungless salamanders (genus Plethodon) are by far the most common vertebrates in the Appalachians. Redback salamanders have been found in densities ranging from 800 to 8,000 salamanders per acre (or 10 per square yard)! Some studies have found that the biomass of red-backs is twice the biomass of all birds and equal to the biomass of all small mammals! One of the adaptations such numbers of these salamanders has mandated is that the red-back salamander emits hormonal scents that mark their territories to others and through aggressive behavior, which aids in their defense. Their superior olfactory sense also enables them to smell their motionless insect prey.
Interesting thing about the redbacks is that they come in two color phases, or morphs. One has the distinctive red (or chestnut brown) stripe on the back, while the other morph does not have the stripe, sporting only the dark gray back. These two phases are often found together, like a blonde and a brunette.
The Appalachians host a diverse and complex salamander population with many species found here and nowhere else in the world (endemic species). This is due to both the age of the Appalachians and the manner in which deep valleys separate ridges and isolated peaks. Over time, these isolated salamander populations evolve their own characteristics and become their own species, no longer able to breed with the divergent populations from other geographic areas. In fact, of our 34 species of Appalachian salamanders, a dozen or so endemic species exist in our Appalachian region. One, the Shenandoah salamander, is found only on talus slopes on three mountain summits in the Shenandoah National Park. Other endemics include the Cheat Mountain salamander and the Peaks of Otter salamander. In each of these cases, these endemics are trapped in isolated populations, surrounded by the common redback salamander, who is making in-roads into their shrinking habitats.
It is believed that the lungless Plethodontidae family had their origin here in the Appalachians as fresh water lunged inhabitants. Finding the cool, fast moving areas of the mountain streams to be the best location for oxygen and food, the buoyant lungs proved a liability. Thus, over time, those with smaller lungs had a distinct advantage over their competitors. Eventually, not only did the Plethodons lose their lungs, many of them migrated onto the terrestrial habitat. Being amphibians, they needed water to release their eggs. However, further evolution enabled many of these species to create a watery gelatinous covering around the eggs that provided an aquatic environment far from a natural body of water. Thus, many salamanders, including the redback, lay her 5 to 12 eggs under logs or rocks in a moist location.
However, the female does not always lay her eggs immediately after picking up the male's spermatophore. Instead, she may retain the sperm for several weeks or months, even over the winter, laying her eggs in the spring. This salamander lacks the aquatic larval stage typical of other salamanders as the larvae pass through the gill stage in the egg. Within three weeks of hatching, juvenile redback salamanders look like small versions of the adult. The juveniles remain on land and reach sexual maturity in 1 to 2 years. When she lays eggs, she will guard them for two months until they hatch, coiling her body around them and turning the eggs routinely to prevent yolk stratification, cause of low birth rates.
Respiration in these lungless salamanders is achieved by oxygen uptake and carbon dioxide diffusion through the skin. Such diffusion only works with a large ratio of surface area to body size. Thus, salamanders have a hot dog shape. The larger the salamander, the larger the surface area it needs. The ultimate expression of this adaptation is the 24 inch long hellbender, found in the Susquehanna and Ohio River drainage basin - which includes most of West Virginia streams and the New River in Virginia and North Carolina - whose large size requires it to have a number of skin folds.
Salamanders are amphibians, like toads and frogs. This means, they also have immature larvae, also known as tadpoles. You can tell salamander tadpoles from frog and toad tadpoles by the large external branched gills on the salamander tadpoles. Salamander larvae have teeth (being carnivorous), but the frogs have horny rasps (for cutting vegetation, being vegetarians – as tadpoles) and salamander larvae grow all four legs early on, whereas frog tadpoles, at most, have only the back legs developed.
Like the viceroy butterfly mimics the toxic monarch butterfly for protection, the same mimicry exists within the Plethodon family. In this case, it is the tasty imitator salamander that wants to mimic the foul-tasting Jordan’s salamander. But it gets interesting how it works. The Jordan’s salamander has several distinct isolated populations, some with red cheeks, some with red legs, and some with neither. The imitator also has the same color options, but when found with red-cheeked Jordan’s, the imitator will only have red cheeks, and when found with the red-legged Jordan’s, will only have red legs!
Our redback salamander also has a third color form that serves as a protective mimicry. In this case, the red-backed has an all red phase, which mimics the toxic red-spotted newt.
Taxonomists have always debated on the classification of many of our Appalachian salamanders. Like so many plants and some animals, some species do mate with other species, creating hybrids and, what is known as hybrid swarms, when a range of variants are known to exist. The crosses of the Jordan’s and slimy salamanders are a good case of this hybridization confusion.